Active ice-phobic freeze point reducing anti-ice coating and method for providing anti-ice protection to surfaces

ABSTRACT

The present invention provides a method for providing anti-ice protection to surfaces, particularly aerodynamic surfaces, to prevent foul weather icing for extended periods of time and over repeated icing situations, comprising applying an organic polymer matrix layer to the surface where the organic polymer matrix layer comprises a homopolymer comprising up to 50% porous polymer solids having a pore size of up to 100 Angstroms and being capable of absorbing and chemically bonding an aqueous freeze-point depressant solution in amounts of up to 99.75% by weight.

FIELD OF INVENTION

The present invention is directed towards a surface preparation in theform of a coating, an adhesive backed film, a vacuum deposited, sprayedor painted aggregate or otherwise applied anterior polymer componentlayer containing an anti-freeze fraction formulated, compounded,constructed and applied so as to lower the freezing point of criticalice-borne surfaces and a method for providing anti-ice protection tosuch surfaces. The deposited and renewable surface treatment willprovide a useful benefit to eliminate, reduce or retard ice formationfor single and repeated icing events on affected surfaces found onmaterials as diverse as airfoils, wind turbines, electrical transmissiontowers, rocket boosters, engine casings, wind screens, ground stations,building materials, freeze-protection blankets, and other foul weatheruse areas for extended periods of time without reapplication.

BACKGROUND OF INVENTION

Ice accumulation on surfaces consists of two treatable areas. The firstis ice removal (deicing) which occurs by application of various deicingfluids or thermal or mechanical methods. The present inventionaccomplishes a second different function of ice prevention (anti-icing)the merits of which can be found on the ground as well as with in-flightaerospace use as well as with other surfaces of structures able tobenefit by protection from freezing precipitation and other foul weathericing events. The purpose of this invention is to lower the freezingpoint of the metal surfaces on aircraft, rocket boosters and enginecasings, as well as ground structures susceptible to ice accumulationfrom single and repeated icing events, such as power transmissiontowers, satellite tracking stations, metal equipment framework, cables,etc. The anti-icing function is accomplished by placing an aqueousfreeze-point depressant solution in the absorbent fraction of a filmsuitably bonded to the surface of a structure so as to allow it to bemaintained under adverse conditions of freezing rain, ice, snow, wind,air speed, temperature and time.

Fluids used for deicing and anti-icing typically are comprised of ablend of water and ethylene glycol or propylene glycol, in a ratio thatranges from 50:50, water to glycol, to about 20:80. They serve to lowerthe freezing point of water in the same manner that similar solutionsprovide anti-freeze protection in automobiles. For the purpose of thisapplication the terms deicing fluid, anti-icing fluid and freeze-pointreduction or depressant fluid will be used interchangeably. These fluidsare sometimes diluted with water in the end use to match the weatherconditions. Deicing fluids melt the frost, snow, or ice which hasaccumulated on, for example, aircraft surfaces, while the aircraft is onthe ground, as well as provide protection against further accumulationand/or refreezing when no further precipitation occurs. Commonly sprayedon under pressure, the fluid melts the ice and snow while the force ofthe spray clears the surfaces. In the case of an aircraft, the formationof ice would change the aerodynamic flow characteristics of, forexample, the wing of the aircraft and prevent its normal functioning.When these fluids are thickened, they provide an extended period ofprotection against frost, snow, and ice, i.e., an extended holdover timewhile the aircraft is on the ground, by remaining on the aircraft untiltake-off, and come off the surfaces when the aircraft becomes airborne.Such fluids are represented by U.S. Pat. No. 4,744,913, Salvador, etal., U.S. Pat. No. 5,118,435, Nieh, U.S. Pat. No. 5,461,100. Jenkins,U.S. Pat. No. 5,653,054, Savignano, et al. and U.S. Pat. No. 5,708,068,Carder, et al.

Deicing or anti-icing fluids have been classified as two types:unthickened and thickened. Unthickened deicing fluids are generallyclassified as Type I fluids, and are comprised of a blend of water andethylene glycol or propylene glycol, in a ratio of about 20:80, water toglycol. They melt the frost, snow, or ice which has accumulated on theaircraft surfaces while the aircraft is on the ground. However, they donot provide adequate protection from further ice and snow formation.They mainly provide protection against refreezing when no furtherprecipitation conditions occur.

Thickened deicing or anti-icing fluids, which have a ratio of about50:50, water to glycol, are classified as either Type II or Type IVdeicing fluids. They prevent ice and snow from forming on aircraftsurfaces that remain on the ground for longer periods of time beforetake-off. Because they are thicker and more viscous, they remain on theaircraft until take-off rather than tending to flow off relatively soonafter application as with Type I fluids. The thickened fluid is appliedon to the aircraft surfaces after snow and ice have been removed, andsnow and ice will then form on the coating, not on the aircraftsurfaces. The thickened deicing coating is then removed from theaircraft by the shearing action during take-off when the aircraftreaches about 70 m/sec or 157 miles per hour. In neither case is longterm protection against ice formation provided, even during flight,because the Type I through Type IV fluids eventually flow off of or areremoved from the aircraft surfaces during take-off by airflow over thesurfaces.

Deicing and anti-icing protection during flight have typically beenprovided by various means such as directed flow of engine exhaust orheat, electrical heaters built into or bonded to aircraft surfaces, orby providing a surface on an aircraft wing which can be selectivelyinflated and deflated to break up any ice formation. All of these addweight and complexity to aircraft systems and, in some cases, requirethat aerodynamic surfaces be reengineered to accommodate changes inairflow which cause changes in lift characteristics. Such mechanical,electrical and pneumatic ice removal systems are represented by U.S.Pat. No. 5,813,631, Butler, et al., U.S. Pat. No. 6,194,685, Rutherfordand U.S. Pat. No. 6,352,601, Ray.

What is needed is a means to provide anti-icing protection to surfaces,particularly aircraft surfaces, which is lightweight and simple to applyand does not require additional complex mechanical and electrical means.A preferred form would be a coating which can be applied to surfaces asneeded and which is highly absorbent of standard deicing and anti-icingsolutions and has the ability to retain such fluids within the absorbentmaterial under high load or wind conditions, i.e., while in flight, toprovide extended time anti-icing for such surfaces.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a freeze-pointreducing method for single or repeated icing events comprising providinga freeze protection composite on a surface to be protected where thecomposite comprises a super absorbent polymer applied to the surfaceproviding a continuous absorbent coating on the surface, and an aqueousfreeze-point depressant solution applied to the super absorbent polymercoating whereby a content of at least 50% of the freeze-point depressantsolution is absorbed and held by the super absorbent polymer providingfreeze-point reduction throughout single or repeated icing events.

Another object of the present invention is to provide an anti-icing filmcomprising a polymer film substrate having a first side and a secondside, an adhesive agent on the first side and a super absorbent polymerlayer on the second side, wherein the super absorbent polymer is capableof absorbing and holding at least 50% of an aqueous freeze-pointdepressant solution and wherein the anti-icing film is applied to asurface to prevent ice formation thereon.

A further object of the present invention is to provide a method forproviding anti-icing to aerodynamic surfaces to prevent foul weathericing which comprises applying an organic polymer matrix layer to theaerodynamic surface, the organic polymer matrix layer comprising ahomopolymer comprising 1 to 50% porous polymer solids having a pore sizeof up to 100 Angstroms which is capable of absorbing and chemicallybonding an aqueous freeze-point depressant solution in concentrations offrom 50-99.75% by weight, whereby the freeze-point depressant solutionis maintained on the aerodynamic surfaces for extended periods of time.

A still further object of the present invention is to provide a methodof applying anti-icing protection to a surface comprising:

cleaning and degreasing the surface,

applying a hydrophilic polyacrylic coating to the surface, wherein thehydrophilic polyacrylic coating comprises a homopolymer having a waterto solid ratio when hydrated of at least 1:1 and a water content whenhydrated of from 50-99.75%.

These and other objects are achieved by applying a coating of amacroporous hyperhydroxy porous polymer material prepared bypolymerizing a mixture of from 40-60 parts by weight of a purifiedmonoester of a hydroxyalkyl acrylate having a single olefinic doublebond and 40-60 parts by weight of a methacrylic acid with up to 5 partsby weight of a polymerization initiator. The resulting molar ratio ofthe monoester to the methacrylic acid is from 1:1 to 2.3:1 which resultsin a polymer that is extremely hydrophilic, having a water content, whenfully hydrated, of 90-99.75%. Since deicing and anti-icing fluids areaqueous solutions, the polymer exhibits a great affinity for such fluidsand is capable of absorbing and retaining such fluids for an extendedperiod of time under adverse conditions.

The polymer can be formed as particles or granules and applied to asurface that has been treated with an adhesive agent by spraying,painting or other application means to form a coating of hydrophilicparticles on such a surface to which an aqueous freeze-point depressantsolution can be applied thereby hydrating the polymer to its maximum.Alternatively, the polymer can be formed as a continuous film coatingapplied to such surfaces either by direct polymerization in situ with orwithout an adhesive agent, or as an anterior or outer layer of amulti-layer film structure which is applied to the surface to form anabsorbent coating thereon with the polymer hydrated by an aqueousfreeze-point depressant solution.

By application of the polymer to aircraft surfaces and hydration withstandard aircraft deicing solutions, anti-icing of such aircraft can beobtained for longer periods of time than the use of deicing oranti-icing fluids alone resulting in lower volumes of the fluids usedwhich translates to cost savings for airlines and airports. In addition,because the coating is of a minimal thickness, is securely applied tothe aircraft to withstand wear under operating conditions and isextremely hydrophilic so as to retain the deicing or anti-icing fluid,it provides extended deicing and anti-icing capabilities while in flightwithout adversely affecting the aerodynamic properties of wings andother aircraft surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of the anti-icing coating of the presentinvention in its simplest form comprising the super absorbent polymerapplied to a surface with an adhesive agent.

FIG. 2 is a cross section of the anti-icing coating of the presentinvention in the form of a multilayer film comprising the superabsorbent polymer applied to a polymer film substrate and secured to asurface with an adhesive agent.

FIG. 3 is a cross section of the anti-icing coating of FIG. 2 with anadded protective mesh over the super absorbent polymer layer.

FIG. 4 is a cross section of the anti-icing coating of FIG. 1 with anadded protective mesh over the super absorbent polymer.

FIG. 5 is a perspective view of the anti-icing coating of FIG. 3 appliedto a wing surface and showing the individual layers in greatly enlargedform.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides anti-ice protection by applying apolyacrylic or other absorbent or superabsorbent coating on surfacesrequiring anti-ice protection. When combined with an aqueousfreeze-point depressant solution absorbed by the absorbent layer, theresulting film provides protection from freezing precipitation andrepeated icing events. Although any absorbent or superabsorbent porouspolymer may have potential and be used as the absorbent layer, preferredpolymers are polymers of functional acrylic monomers which are combinedto form a polymer skeleton providing a high number of hydroxyl sites.One such polymer which is particularly preferred is a macroporousabsorbent fraction formulated as described in the inventor's prior U.S.Pat. No. 6,201,089 and U.S. Pat. No. 6,326,446, both of which areincorporated herein in their entirety by reference thereto.

In its preferred form, the macroporous polymer used as thesuperabsorbent layer comprises:

a) 40-60 parts by weight of a purified monoester of a hydroxyalkylacrylate having a single olefinic double bond,

b) 40-60 parts by weight of a methacrylic acid,

c) up to 5 parts by weight of a polymerization initiator, wherein themolar ratio of the purified monoester of hydroxyalkyl acrylate to themethacrylic acid is from 1:1 to 2.3:1, and the polymer is capable ofholding 90-99.75% water.

The polymer is produced from a monomer mixture comprising 40-60 parts byweight of a purified monoester of a hydroxyalkyl alkyl acrylate having asingle olefinic double bond, 40-60 parts by weight of a methacrylicacid, and 0.001-5 parts by weight of a polymerization initiator by:

a) mixing substantially similar fractions of a purified monoester of ahydroxyalkyl acrylate having a single olefinic double bond and amethacrylic acid with a sufficient amount of a polymerization initiator,

b) holding the mixture under polymerization conditions to form a polymergel, and

c) casting the polymer gel to shape,

whereby the polymer or an article formed therefrom is capable of holding90-99.75% water. Polymerization is accomplished by conventionaltechniques such as bulk polymerization, solution polymerization,suspension polymerization or emulsion polymerization. The polymerizationtechnique used is dependent upon the volume of polymer required and thenature of the final product being produced. The resulting product is astereospecific isotactic heterogenous copolymer product of a thermosetresin hydrogel in which the molar ratio of monoester to diester iswithin the range of 1:1 to 2.3:1, preferably 1.5:1, and wherein the porediameter of the polymer is greater than 90 Angstroms.

As the monoester of a hydroxyalkyl acrylate having a single olefinicdouble bond, acceptable compounds include, but are not limited to,2-hydroxyethyl methacrylate, glyceryl methacrylate, 2-hydroxypropylmethacrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, and2-hydroxypropyl acrylate. Acceptable methacrylic acid, includes,dimethacrylates.

The polymerization initiator may depend on the method of polymerizationor the final intended use of the polymer. For example, where the polymeris to be formed as a solid object, free radical initiators may be used.Preferred initiators of that type include difunctional polyesters suchas 2,5-Dimethyl-2,5-bis(2-ethylhexoylperoxy)hexane, or tertiarybutylperoxypivilate. Alternatively, where the ultimate use of the polymer isas a coating applied in the form of the monomer mixture and polymerizedin situ, the initiator may be radiation activated such as UV catalysts2,2-Azobis(2-methylpropionitrile) or azobisbutyronitrile (AIBN). Theinitiators are not restricted to use in a particular polymerizationmethod or for a particular final product. For example, the free radicalinitiators may be employed in coatings and the radiation activatedinitiators may be employed in the formation of solid articles.

In addition to the substantially similar fractions of the monoester andthe methacrylic acid, the monomer mixture may be enhanced with traceamounts of a longer chain alkyl acrylate or methacrylate ester comonomersuch as cyclohexyl methacrylate, trimethylolpropane trimethacrylate orethyleneglycol dimethacrylate. Such additional comonomers enhance thepolymer crosslinking for situations where added polymer strength isdesired. The trace amounts of these comonomers are generally less than0.1% by weight of the total monomer mixture.

The hyperhydroxy polymer of the present invention can be formed toproduce an article which is sufficiently crosslinked by intrinsic actionthat the resulting article requires no additional crosslinking monomers.For example, a polymer comprising 2-Hydroxyethyl methacrylate 100 ml(50%) Methacrylic acid 100 ml (50%) 2,5-Dimethyl-2,5-bis(2-ethylhexoyl-4drops (0.0005%) peroxy)hexane.

The monomer mixture is prepared and polymerized using the method of bulkpolymerization and is cast in the desired form in an industrialconvection oven at 90° C. for 30 minutes. Following this, the polymer isannealed in the oven at 110° C. for six hours. When the polymer isimmersed in a buffered solution of 0.9N saline and equilibrated in a0.9N Sorenson solution, it exhibits a saline content of 95% and a waterto solid ratio of 19:1.

The particular properties of the polymer produced in this example arerepresented as follows:

Water Content: 95% 0.9% N saline solution @ 25° C.

Index of Refraction: 1.50-dry @ 25° C.

1.33-wet @ 25° C.

Linear Expansion Ratio: 2.35 @ 25° C.

Hardness: >90 (ASTM/Durometer) uniform hardness from a blank top tobottom and center to edge

Elongation to Break: Exceeds 160% of hydrated diameter

Weight: (Dry) 0.8 Gram/Unit Blank (6.0 mm.times.11.5 mm)

Infrared spectra of the polymer obtained by Fourier Transform InfraredSpectroscopy (FTIR) measured across the range of 4400 to 450 cm⁻¹ showbands in the region of 3200 to 2500 cm⁻¹ which is characteristic of O—Hstretching vibrations from hydroxyl groups, a band of 1710 to 1720 cm⁻¹characteristic of C—O stretching vibrations from ester carbonyl groupsand strong bands in the region of 1100 to 1300 cm⁻¹ characteristic ofC—O stretching vibrations in esters. These bands characterize thepolymer as belonging to the polyacrylate group but one which contains anunusually large number of hydroxyl groups which allow the polymer toreadily absorb and hold water or aqueous solutions rendering it highlyadvantageous for the present invention.

Swelling upon hydration is small but noticeable (less than 10% change inlinear dimension) corresponding to about a 25% volume increase. Wateruptake by the resin under 100% relative humidity is on the order of 40%by weight. Despite the high water uptake by the polymer, the spectrachange very little between the dry condition and the hydrated conditionat 100% relative humidity. Under saturation, the peak at about 3500 cm⁻¹which represents hydroxyl and water increases in width. Resaturating andredrying the polymer makes minimal changes to the infrared spectra.

The infrared spectra and weight measurements indicate that the polymercan reversibly adsorb and desorb water like a sponge without any changein its chemical characteristics. In addition, the physicalcharacteristics remain unchanged, i.e., the polymer does not crack ordissolve. Even when dry, the spectra indicate a large amount of freehydroxyl and/or water.

By incorporating a non-reactive diluent in the monomer mixture, thepolymer can be produced with significantly higher expansion and swellrates using solution polymerization techniques. Thus, in the followingexample, a polymer having a water to solid ratio of 399:1 can beproduced. 2-Hydroxyethyl methacrylate 100 ml (25%) Methacrylic acid 100ml (25%) 2,5-Dimethyl-2,5-bis(2-ethylhexoyl-peroxy)hexane 4 drops(0.0005%) 1,4-Butanediol (diluent) 200 ml (50%)

The monomer/diluent solution is cast into a solid, film, sheet ormembrane in an industrial convection oven at 90° C. for 30 minutes. Uponremoval from the oven, the non-reactive diluent fraction is removed byextraction with water and the remaining polymer is either dried orequilibrated in solution as needed for the final article. Since thediluent is non-reactive, it forms no part of the final polymer. Rather,its role is in the nature of a spacer to spread the crosslinking of thepolymer thereby increasing the number of hydroxyl sites available in thepolymer skeleton. The result is a polymer structure capable of increasedhydration and expansion with an even higher water to solid ratioresulting in a water content of up to 99.75%.

The solid polymer produced in this manner can be granulated for use in amethod where the polymer is applied to an adhesively prepared surface byvacuum deposition, spraying, painting or mechanical distribution or itcan be produced as films or sheets for use with or without an additionalsubstrate film.

The suitability of the solid polymer as an absorbent for aqueousfreeze-point depressant solutions is shown by a simple freezer test.Granules of the solid polymer were prepared as above and were dehydratedto ensure full availability of the hydroxyl bonding sites to thehydrating solution. Equal weight portions of the granules were thenfully saturated in 50% and 100% solutions of propylene glycol. One halfof each batch of saturated granules was transferred to a laboratory dishand placed in a freezer at −20° F. for overnight storage while theremaining half of each batch was maintained at room temperature. Directobservation of each batch the following day showed no difference betweenthe granules stored at sub-freezing temperatures and those maintained atroom temperature. In both cases, the granules retained their absorbedglycol solution while the granules stored at sub-freezing temperatureremained unfrozen and evidenced no ice crystal formation.

By incorporating a radiation activated polymerization initiator, such asa photocatalyst, in a solvent free casting method the polymer may becoated and polymerized in situ on surfaces to be protected against iceformation. The following is an example of such a polymer which includesa trace amount of a longer chain ester crosslinking comonomer.2-Hydroxyethyl methacrylate 650 ml (49.96%) Methacrylic acid 430 ml(49.96%) Cyclohexyl methacrylate 1 ml (0.075%)2,2-Azobis(2-methylpropionitrile) 5 gm (0.50%)

The monomer mixture is poured, sprayed or otherwise applied to a surfaceor a chosen mold and is irradiated with ultraviolet light in the 320-380nm range at room temperature. Other radiation sources, such ascobalt-60, may be used depending on the specific nature of thepolymerization initiator. Cure rates for radiation catalyzed polymersare a function of the surface thickness, monomer activity and radiationintensity. Radiation catalysis of the monomer mixture is particularlyuseful where the polymer is desired to be formed in situ as a coating onan existing structure.

A protective u.v. blocking additive of about 0.01 percent to 25 percentof a substituted 2-phenyl benzotriazole containing a styrene group orrelated functional u.v. absorbing compound is preferably added to theabsorbent polymer formulation to improve chemical stability and coatinglife cycle. Physical properties including optical properties,absorbency, particle size, And mechanical properties @RT, 65° F. to 165°F., elastic modulus (tension and compression), Shear modulus, Poisson'sratio, strain to failure, ultimate strength, coefficient of thermalexpansion, and density, as well as processing data as relating totemperature and viscosity are determined by standard analyticaltechniques.

In the method of the present invention, the super absorbent polymer isapplied to a surface to be protected by one of several means to producea coating which is then hydrated by an aqueous solution of freeze-pointdepressant such as ethylene glycol, propylene glycol, sodium citrate, orthe like. As noted, the present method may be applied to any surfacewhich may need protection from foul weather icing and is particularlyapplicable to aircraft surfaces due to the light weight of the materialsand the relatively low thickness of the coating such that theaerodynamic characteristics of those surfaces are not adverselyaffected. Indeed, it is believed that the present method and thecoatings or films employed may improve the performance of airfoil liftsurfaces. Preliminary investigation indicates that the surface-to-volumeratio of the aqueous freeze-point depressant in the polymer acts toreduce friction at the surface of the polymer thereby promoting laminarair flow. Anticipated benefits of such improved surface flow dynamicsinclude increased lift, reduced drag, lower fuel consumption, increasedoperating range, etc.

In a first embodiment, the polymer formulation described above iscompounded in the form of a block polymer, graft polymer using apolyolefin or other suitable polymer film substrate to produce aflexible multilayer film, graphically represented in FIG. 2, comprisinga posterior substrate 203 and an anterior absorbent polymer layer 204which can be applied to surfaces 201 and then hydrated with an aqueousfreeze-point depressant solution. Representative polymers for thesubstrate 203 include, but are not limited to, polyalphaolefins and highdensity polyethylene (HDPE) films having a thickness of about 30microns. The polyolefin or other substrate film 203 may be surfacetreated with gamma radiation or other suitable procedures to improvebonding to the absorbent layer 204 and to a surface 201 with an adhesiveagent 202 which is evenly applied to the substrate film 203, or to thesurface 201 on which the film is to be applied, using conventional orvapor deposition methods. Depending on the adhesive agent used, arelease sheet may be provided to protect the adhesive agent until use.Suitable adhesive agents include, but are not limited to, polymeradhesives such as cyanoacrylate adhesives, alcohol-silane adhesionpromoting coatings or agents such as Bondit A-3 and C-52 obtained fromReltek LLC of Santa Rosa, Calif., or custom, proprietary adhesive agentsbased on those formulas, and other adhesives or adhesive agents suitablefor use in low temperature, high wind speed and other foul weatherconditions. When in place on the surface 201, the anterior absorbentlayer 204 is then prepared to maximum absorbency using a propyleneglycol, sodium citrate or other aqueous freeze-point depressantsolution. As the freeze-point depressant solution, any of the FAAapproved Type I to Type IV fluids may be used. Preferred fluids are TypeI to Type IV propylene glycol or sodium citrate aqueous solutions.

As noted, the anterior absorbent polymer layer 204 may be directly castand polymerized on the substrate film 203 in which case the substratefilm 203 is prepared by appropriate means to receive the anteriorpolymer layer 204. This preparation may include procedures to promote asecure mechanical interface between the substrate 203 and the polymerlayer 204 as the latter undergoes polymerization. Alternatively, thesurface of the substrate film 203 may be prepared to promoteco-polymerization with the anterior polymer layer 204 providing a secureadherence of the anterior polymer layer 204 and the substrate film 203at the molecular level. As a further alternative, the substrate film 203and the anterior polymer layer 204 may be cast simultaneously andco-polymerized or they may be cast and polymerized separately andsecured together as a laminate using appropriate adhesives or adhesiveagents.

Film construction is based on physical and performance requirements. Keyelements of that construction are the functional variables of exposedsaturated absorbent polymer, skeleton vacuole area, ratio of exposedabsorbent polymer to percent skeleton coverage area, absorbent polymerlayer thickness, percent swell of the absorbent polymer as well asstretch and shear factors which are adjusted which are adjusted andcoordinated to provide maximum performance demands of the chosensubstrate. Testing of selected samples is conducted by coating andtesting aluminum alloy test plates 10 cm×30 cm in accordance withrecommended test protocols set forth by Anti-icing MaterialsInternational Laboratory, Chicoutimi, Quebec (AMIL). Selected testsample coatings vary by thickness (thin/thick), absorbency (50%swell/100% swell) and anti-freeze fraction (propylene glycol/sodiumcitrate). Standardized additional material characterizations include thefollowing: solute bond stability and preliminary wear and weatherabilityindicators such as tensile strength, shear and other indicatorsinfluencing life cycle. The following are examples of anti-icing filmsaccording to the present invention:

Example 1

Anterior Absorbent Layer Composition Crosslinked hydroxypolymer of: 50%2-hydroxyethyl methacrylate 50% methacrylic acid Thickness 100 micronsWater:Solid ratio 99:1 Pore size 100 Angstroms Absorbency 100% HydratantPropylene glycol Posterior Substrate Layer Composition PolyolefinThickness 30 microns

Example 2

Anterior Absorbent Layer Composition Crosslinked hydroxypolymer of:97.75% 2-hydroxyethyl methacrylate 2% methacrylic acid 0.25% crosslinkerThickness 50 microns Water:Solid ratio 1:1 Pore size 10 AngstromsAbsorbency 50-55% Hydratant Sodium citrate Posterior Substrate LayerComposition Polyolefin Thickness 30 microns

Example 3

Anterior Absorbent Layer Composition Crosslinked hydroxypolymer of: 50%2-hydroxyethyl methacrylate 50% methacrylic acid Thickness 50 micronsWater:Solid ratio 99:1 Pore size 100 Angstroms Absorbency 100% Hydratantpropylene glycol Posterior Substrate Layer Composition PolyolefinThickness 30 microns

Appropriate physical methods, i.e., direct in situ polymerization,adhesive, adhesive agent, are used to apply the complete anti-icing filmas described onto the structural surfaces where anti-icing protection isdesired. The film may be applied dry, that is without absorbedhydratant, and then hydrated with the desired aqueous freeze-pointdepressant solution, or it may be applied in pre-hydrated form.Following application the surface is able to maintain a lower surfacetemperature to prevent icing. Efficacious use and performance of thefilm can be determined using the following standard static performancetest methods and procedures designed and conducted by the Anti-icingMaterials International Laboratory (AMIL) at the University of Quebec atChicomuni

1. Water Spray Endurance Tests (WSET)—This test is conducted accordingto methodology used by the Automotive Engineers SAE Aerospace StandardA55901 used to qualify aircraft anti-icing fluids by Aerospace MaterialsSpecification AMS1428E. This test is run for approximately 4 hours andat least one WSET test is modeled to compare the test sample with thecurrent fluid technology.

2. A High Humidity Endurance Test—This test is also required byAMS1428E. The test simulates the overnight exposure of an aircraft onthe ground in open air with relative high humidity with actualtemperature of the aircraft below freezing.

3. Ice Accumulation Tests (Static Adhesion Tests)—This test method wasdeveloped to evaluate the ability of solid icephobic coatings to preventice formation on surfaces at different angles. The icing can beseparated from a cold room simulating a freezing precipitation. Thistest is run at two temperatures.

4. Centrifuge Adhesion Tests (CAT)—This test is used to evaluate theability of a solid coating to reduce the adhesion of ice to a surface.

5. Based on the test results of 1-3, repeat testing is conducted todetermine how many cycles of deicing the coating can undergo and remainactive in anti-icing.

Following elapsed time of the decay of the film, the surface can bedebrided, retreated and the film reapplied. Standard maintenanceprocedures are constructed to provide specific inspection, measurementand testing methods for decay and life cycle identification.

In a second embodiment, graphically shown in FIG. 1, the anti-icingcoating is prepared from and comprises a macroporus polyacrylicthermoset or thermoplastic absorbent or superabsorbent polymer materialprepared as described in the first embodiment and thereafter processedinto micron to granule size particles able to complete uptake or fullabsorbtion under load of an aqueous freeze-point depressant solution,e.g. propylene glycol, sodium citrate, etc. The particles have a size offrom 0.1 to 0.5 mm, preferably 0.1 to 0.25 mm so as to be sprayable andto form a thin coating 103 when applied to a surface 101. Usingcompressed gas spray deposition or other suitable delivery means thisantifreeze gel is applied to a surface 101 to be treated, such as anairfoil, electrical transmission towers, cables, ground stations, windturbines, building surfaces, etc., and to which, preferably, a Mach One(for airfoil use) adhesive or adhesive agent 102 has been applied. Aspreviously identified, suitable adhesives or adhesive agents are thosewhich can reliably adhere the polymer to the surface without adverseeffects on either and include, but are not limited to, polymer adhesivessuch as cyanoacrylate adhesives, alcohol-silane adhesion promotingcoatings or agent such as Bondit A-3 and C-52 obtained from Reltek LLCof Santa Rosa, Calif., and other adhesives or adhesive agents suitablefor use in low temperature and high wind speed conditions. When preparedunder specialized and controlled conditions and hydrated with an aqueousfreeze-point depressant fluid the resulting coating 103 acts to freezeprotect those surfaces 101 just described in the same manner as the filmembodiment of FIG. 2, by providing and maintaining a quantity of thefreeze-point depressant solution absorbed by the polymer so as tocontact any freezing or frozen precipitation impacting the surface. Ifdesired, an amount of adhesive or adhesive agent can be mixed with theparticles to promote interparticle adhesion upon application.Preferably, such adhesive or adhesive agent is the same as that appliedto the surface and is one which remains on the surface of the particles,is not absorbed by the polymer and does not block the pores of thepolymer to prevent hydration of the polymer by the aqueous freeze-pointdepressant solution.

The resulting coating has a thickness greater than one particle diameterand will protect a surface from freezing precipitation for repeatedicing events. Efficacious use of the coating can be determined usingstandard and custom test methods and procedures designed and conductedby the Anti-icing Materials International Laboratory at the Universityof Quebec at Chicomuni.

In a third embodiment an alternate anti-icing film to the compoundedcomposite film described in the first embodiment is provided. Thecarrier fraction anterior layer formulated as in the primary embodimentis formed and polymerized and is then bonded to a polyolefin or othersuitable flexible film using a chemical adhesive or adhesive agents aspreviously identified and procedures such as to resist degradation fromfreezing precipitation and repeated icing events. This film structure issimilar to that shown in FIG. 2 with the addition of an adhesive layerbetween the substrate 203 and the polymer layer 204.

The material must pass the previously described static performance testsof the anti-ice capability of the complete anti-icing film.

As a further embodiment, an additional surface treatment is applied tothe anterior layer 204 of the film of the first embodiment, the coating103 of the second embodiment or the film of the third embodiment and isgraphically illustrated in FIGS. 3 and 4. A semipermeable thermosetthermoplastic or other suitable material is nanolayered, scaffolded,vapor deposited, grafted, block polymerized or otherwised attached tothe surface of the absorbent polymer film or coating 304, 403. Thissurface layer 305, 404 is constructed to improve weatherability, lifecycle, foreign object damage protection and to maintain stability of thehydrated polymer fraction 304, 403 below it. This layer 305, 404 ispreferably in the form of a hydrophobic, ice-phobic mesh or net over theabsorbent polymer 304, 403 and is prepared from materials such as acarbon composite treated by trimethylhydroxysilane. As a mesh or net,this layer 305, 404 serves as an exoskeleton and provides physicalprotection to the absorbent polymer 304, 403 while permitting theabsorbed freeze-point depressant to contact freezing or frozenprecipitation and to be re-applied and absorbed by the underlyingabsorbent polymer. In this respect, the mesh size can be varied based onoverall performance requirements to meet desired conditions, includingthe type of freeze point depressant used. In this manner, the ratio ofexposed absorbent polymer to percent skeleton coverage of the mesh canbe determined for optimum anti-ice capability. Because of the meshstructure of this layer 305, 404, even though it is hydrophobic orice-phobic, it does not interfere with the aqueous freeze-pointdepressant solution. However, the hydrophobic or ice-phobic nature ofthe protective mesh does assist in preventing formation of ice on thecoating. The surface 301, 401, adhesive layer 302, 402 and polymer filmsubstrate 303 of FIGS. 3 and 4 correspond to the respective elements ofFIGS. 1 and 2.

In use, application of the coating to a surface is relatively simple.For each embodiment, the surface, i.e., a wing on an aircraft, is firstcleaned and degreased by normal methods to prepare the surface. Wherethe super absorbent polymer coating is to be applied in particle orgranular form, an adhesive agent is then applied to the surface and theparticles of the polymer are applied by spraying or otherwisebroadcasting the particles onto the adhesive surface. Where the superabsorbent polymer is applied by in situ polymerization, the monomermixture with a polymerization initiator is spray coated, poured orpainted onto the cleaned and degreased surface and the polymerizationinitiator is activated to polymerize and crosslink the monomers therebyforming the porous super absorbent polymer coating. When the superabsorbent polymer is prepared as a preformed single or multilayer film,the surface is prepared as above and the film is laid in place with thesuper absorbent polymer exposed. The film preparations may be providedin a single piece to cover the desired surface, in precut sections basedon the size and shape of the surface which are laid separately to form acomplete coating over the surface, in rolls or sheets of the film whichmay be spread over the surface and cut to fit, or in any other mannercommonly used to apply a film to a surface. Following application, thesuper absorbent polymer is hydrated as needed by application of theaqueous freeze-point depressant solution.

FIG. 5 graphically illustrates an aerodynamic wing 501 on which themultilayer film comprising the polymer film substrate 503, superabsorbent polymer 504 and protective mesh 505 have been applied using anadhesive or adhesive agent 502 as previously described. While thecoating of the present invention may be applied so as to cover theentire aerodynamic surface, in the preferred application, the principalareas to be covered on a wing surface are the leading edge and the upperwing surface from the leading edge rearward approximately one third toone half the depth of the wing. Also, in those embodiments including theprotective mesh 305, 404 and 505, as shown in FIG. 5, the mesh 505preferably extends beyond the edges of the underlying layers so as toprovide protection to those edges, the mesh being secured to the surfacebeing protected by the adhesive agent 102, 202, 302, 402 and 502.

The spectrum of variations of foul weather conditions resulting infreezing precipitation and repeating icing events creates a wide rangeof material surface icing conditions. The embodiments described abovecan be modified in composite construction to improve the economy of usewithout departing from the scope of this invention. Thickness and weightreductions are made to each of the absorbent, substrate, and adhesivelayers so as to match performance to cost for its intended end use. Inaddition UV catalysis and other ambient or room temperaturepolymerization methods are available to improve the economy offabrication and application.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. The method of claim 15 furthercomprising providing a polymer film substrate having a first side and asecond side, an adhesive layer on said first side and said organicpolymer matrix layer on said second side, whereby said organic polymermatrix layer is capable of absorbing and holding at least 50% of anaqueous freeze-point depressant solution.
 10. The method of claim 9wherein said adhesive layer is a pressure sensitive adhesive and saidfilm further comprises a removable release sheet over said adhesivelayer.
 11. The method of claim 10 further comprising a protective meshlayer over said organic polymer matrix layer, said protective meshhaving a porosity whereby said freeze-point depressant solution can passthrough.
 12. The method of claim 9 wherein said polymer film substrateis a polyolefin.
 13. The method of claim 9 wherein said organic polymermatrix layer comprises a continuous polymer of cross-linked acrylicmonomers and methacrylic acid.
 14. The method of claim 11 wherein theprotective mesh is a carbon composite treated withtrimethylhydroxysilane.
 15. A method for providing anti-icing toaerodynamic surfaces to prevent foul weather icing comprising applyingan organic polymer matrix layer to said surface, said organic polymermatrix layer comprising a continuous polymer comprising 1 to 5% porouspolymer solids having a pore size of at least 90 Angstroms being capableof absorbing and chemically bonding an aqueous freeze-point depressantsolutions in amounts of up to 99.75% by weight, whereby saidfreeze-point depressant solution is maintained on said aerodynamicsurfaces for extended periods of time.
 16. The method of claim 15further comprising providing a protective mesh layer over said organicpolymer matrix, said protective mesh having a porosity whereby saidfreeze-point depressant fluid can pass through.
 17. The method of claim16 comprising applying an adhesive agent to said surface and applyingsaid organic polymer matrix as a plurality of macroscopic particleshaving a size of from 0.1 to 0.5 millimeters dispersed over said surfaceto form a substantially continuous coating thereon.
 18. The method ofclaim 16 comprising forming said organic polymer matrix as a continuouspolymer film, providing an adhesive agent on said surface and applyingsaid continuous polymer film onto said adhesive agent.
 19. The method ofclaim 18 further comprising forming said continuous polymer film on apolymer film substrate and applying said substrate onto said adhesiveagent. 20-28. (canceled)
 29. The method of claim 15 comprising formingsaid organic polymer matrix layer as a coating of polymer granules orparticles applied to said surface by vacuum deposition, spraying,painting or mechanical distribution.
 30. The method of claim 29comprising mixing an amount of non-absorbable curable adhesive agentwith said granules or particles, applying said mixture to said surfaceand curing said adhesive agent whereby said particles are adhered tosaid surface and to each other forming a coating of said polymer matrixhaving a thickness greater than one particle diameter.
 31. The method ofclaim 15 comprising forming said organic polymer matrix layer in situ asa film by spray coating, pouring or painting onto said surface a monomermixture and a polymerization initiator and activating saidpolymerization initiator.
 32. The method of claim 15 wherein saidorganic polymer matrix comprises a hydrophilic polyacrylic polymercomprising 40-60 parts by weight of a purified monoester of ahydroxyalkyl acrylate having a single olefinic double bond and 40-60parts by weight of a methacrylic acid.
 33. The method of claim 15wherein said organic polymer matrix further comprises a polyurethane.34. The method of claim 15 wherein said organic polymer matrix furthercomprises a polyacrylic.
 35. The method of claim 30 wherein saidnon-absorbable curable adhesive agent is selected from a polyurethane ora polyacrylic.